1. Field of the Invention
The present invention relates to a semiconductor laser device for use in optical communication devices, optical information reading devices, and the like, and more particularly, to an electrode structure of a laser diode chip that facilitates the inspection process.
2. Description of the Related Art
FIG. 4 is a perspective view showing the configuration of a laser diode chip used in a conventional semiconductor laser device, and FIG. 5 is a cross-sectional view, taken along line B-Bxe2x80x2 of FIG. 4. Referring to FIGS. 4 and 5, the semiconductor laser device comprises an electrode 1 composed of layers made of different materials, a light-emitting section (oscillator) 2 inside a laser diode chip 3, the laser diode chip 3, anode and cathode surfaces 4 and 5 of the laser diode chip 3, a package stem or photodiode 6, a Au wire 7, and a light-emitting end face 8 from which laser light is emitted.
In the laser diode chip 3, one of the anode and cathode surfaces 4 and 5 is joined to the package stem or photodiode 6, and the electrode 1 is formed over almost the entirety of the other surface. The Au wire 7 is joined to the electrode 1 to establish electric contact with the outside.
In the laser diode chip 3 having such a configuration, a power supply is connected between the Au wire 7 and the package stem or photodiode 6, and current is passed through the laser diode chip 3, whereby laser oscillation occurs in the light-emitting section (oscillator) 2, and laser light is obtained from the light-emitting end face 8.
However, since the electrode 1 is formed on almost the entire anode or cathode surface 4 or 5 of the laser diode chip 3, as shown in FIGS. 4 and 5, it is impossible to observe the state of the light-emitting section (oscillator) 2 inside the laser diode chip 3 from the top side by using an optical microscope or an electronic microscope.
In the semiconductor laser device, it is well known that the crystal in the light-emitting section (oscillator) of the laser diode chip may break due to static electrical discharge from the outside, or due to electrical stress, such as surging, and that the crystal may become degraded and abnormal, with shortened service life, while decreasing light output over time as current is applied.
In a case in which the light-emitting section (oscillator) in the laser diode chip breaks or becomes abnormal, and light output decreases, it is effective for finding the cause of the decrease in light output to directly observe the light-emitting section (oscillator) inside the laser diode chip.
Conventionally, the state of the interior light-emitting section (oscillator) can be actually observed only after the electrode is entirely removed by a chemical agent to expose the anode or cathode surface of the laser diode chip, and an electrode is formed again in order to establish electric contact at such a position as not to hinder the observation of the light-emitting section (oscillator) inside the laser diode chip.
Accordingly, it is an object of the present invention to provide a semiconductor laser device having a chip electrode structure that facilitates observation of the interior of a laser diode chip.
In a first aspect of the present invention, a semiconductor laser device having a chip electrode of a semiconductor laser is provided. The laser device includes a first electrode layer of a first material, and a second electrode layer of a second material. The second electrode layer includes an opening corresponding to a light-emitting section of the laser. The second electrode layer is formed on a face of the first electrode layer and the first material of the first electrode layer is different than the second material of the second electrode layer.
In a second aspect of the present invention, a semiconductor laser device is provided. The laser device includes a laser diode chip having a light-emitting section. The laser device further includes a first electrode layer of a first material formed on a face of the laser diode chip. A second electrode layer of a second material is formed on a face of the first electrode layer and has an opening corresponding to the light-emitting section of the laser diode chip. The first material of the first electrode layer is different than the second material of the second electrode layer.
In another aspect of the present invention, a method for forming a viewable semiconductor device having a chip electrode of a semiconductor laser is provided. The method includes the step of providing a first electrode layer of a first material. The method also includes the step of providing a second electrode layer of a second material and having an opening corresponding to a light-emitting section of the laser. The second electrode layer is provided on a face of the first electrode layer and the first material of the first electrode layer is different than the second material of the second electrode layer.
In yet another aspect of the present invention, a method of forming a semiconductor laser device is provided. The method includes the step of providing a laser diode chip having a light emitting section. The method also includes the step of providing a first electrode layer of a first material formed on a face of the laser diode chip. A second electrode layer of a second material is provided, the second electrode layer being formed on a face of the first electrode layer and having an opening corresponding to the light-emitting section of the laser diode chip. The first material of the first electrode layer is different than the second material of the second electrode layer.